It has some use cases but for the most part it's literally a wall of unstructed information. Difficult to parse and build any mental hierarchy.
It's also ... incredibly easy to do with existing css.
care to demonstrate? given a dynamic collection of images where you don't know the aspect ratios beforehand
Where it gets more complicated is getting them all to align horizontally at the bottom, which even this proposal doesn't do. Pinterest, of course, solved this by not having a "bottom."
In the photo demo all content is either 1-column or 2-column wide - and that already results in some very noticeable gaps. I don't get the impression that it can properly handle arbitrary aspect ratios. You're pretty much forced to stick to a single column width and fit all images to match, so not exactly an improvement over what we already have right now.
https://yakubin.com/photography/albumless/
https://yakubin.com/photography/album/kenya-2023/
Proper masonry layouts which fill all available space in practice actually crop some images. Leaving space around photos is required when you don’t want cropping and want to preserve aspect ratio. That’s why I prefer my solution over what JS libraries for masonry layouts do.
In the megamenu demo the multicolumn layout is pretty much indistinguishable from masonry. The only thing wrong with it is that it allows column breaks in the middle of content. That doesn't need masonry to fix it.
In the newspaper demo the multicolumn layout is actually better, because that's how newspapers work. The masonry demo becomes an unreadable mess.
The museum demo almost feels intentionally mis-designed. The CSS Grid 1 layout obviously has issues, but it could've easily been solved by pulling the nav bar out of the gallery, and using a multicolumn layout for the gallery instead.
So that leaves the Pinterest-style photo gallery. Sure, it's objectively better if you want to achieve this kind of style, but it's an outdated design with horrible UX. Why is it special enough that we need explicit support for it in the standard?